1. Field of the Invention
The invention relates to the field of manufactured radio frequency devices. More particularly, the present invention relates to radio frequency shields for use in association with a coaxial connector.
2. Discussion of the Related Art
FIGS. 1-4D show prior art devices. Prior art CATV signal outlets are shown in FIGS. 1, 2, and 4B while prior art coaxial cable connectors are shown in FIGS. 3A-B, 4A, 4C, and 4D.
FIG. 1 shows a front view of a wall mounted coaxial connector 100. The connector 102 is mounted on a wall plate 104 fixed to a room wall 106. As shown, the connector is a female F connector. A hole 108 in an insulator 110 of the connector 102 provides access to a CATV signal conductor 304 (see FIGS. 3A-B) within the connector.
FIG. 2 shows a side view of the wall mounted coaxial connector 200 of FIG. 1. Here, the female F connector 102 is shown as a female-female connector for splicing coaxial cable. Threads at opposed ends of the connector 203, 205 provide a means for attaching male F connectors to opposed splice ends 207, 209. A coaxial cable for carrying a CATV signal 204 is terminated with a male F connector 202 that threadingly engages an end 209 of the splice.
Typical coaxial cable features will be known to persons of ordinary skill in the art. For example, an embodiment includes a center conductor 220 surrounded by a dielectric material 222, the dielectric material being surrounded in turn by one or two shields 224 such as a metallic foil wrapped in a metallic braid. An outer insulative jacket 226 such as a polyvinylchloride jacket encloses the conductors.
As seen, the open end of the splice 207 provides an opportunity for unwanted RF ingress 208. In particular, unwanted RF ingress 206 is shown entering an exposed end of the splice 207 where it is conducted by a CATV signal conductor 204 through the connector and to a signal conductor 220 of the attached CATV coaxial cable.
FIG. 3A shows a cross-section of a splice 300A and FIG. 3B shows a side view of the splice of same splice 300B. Referring to both of the figures, the splice includes a cylindrical outer body 302 with a circumferential, hexagonal grip 304 between opposed first and second ends 322, 324 of the splice. Outer surfaces of the body are threaded, in particular, an outer surface between the first end and the grip ring is threaded 309 and an outer surface between the second end and the grip ring is threaded 311.
Within and at opposed ends of the cylindrical body 304 are insulators 306, 308, each having a central cavity 310, 312 for receiving opposed ends 316, 318 of a tubular seizing pin 394. Resilient tines located in each end of the seizing pin 370, 372 provide a means for making a secure electrical contact with a conductor (not shown) inserted in either end of the seizing pin. Splice internals are typically fixed in place by rolling an end of the body 324. In some embodiments, rolling a body end 324 or an interference fit fixes an annular plug 323 adjacent to the second end insulator 312.
FIG. 4A shows a cross-sectional view of a bulkhead port connector 400A. To the extent that connector internals are insertable from only a single end, the connector may be referred to as “blind.” The connector provides an F female connection such as a threaded port 414 at one end and a mount 403 at an opposed end. The connector includes an electrically conductive body 402, and an internal contact 407 with a trailing portion or terminal 401 electrically interconnected by a link 404. The contact is supported by an insulator 408, 412 that is held in place by a port end lip 405. An aperture 418 in the insulator provides for inserting a coaxial cable center conductor into the port contact 407 and body threads 414 provide for engaging an F male connector having a threaded nut.
The bulkhead port 400A has a mount 403 at one end that may be separate from or include portions of a device/equipment bulkhead or portion(s) thereof. The mount supports the bulkhead port at a base 417. A contact trailing portion 401 passes through a hole in a base insulator 406 and then through a passageway in the base. An airgap and/or insulator may be used to electrically isolate the contact trailing portion from electrically conductive mount.
FIG. 4B shows a coaxial cable drop within a room 400B. As shown, a hole 434 penetrates a room baseboard 432 and a length of coaxial cable 439 enters the room through the hole. Such cable drops are typically terminated with male F connectors. In particular, a male F connector 436 has an outer shell 435 adjacent to a fastener 433 and a prepared end of the coaxial cable is inserted in the connector such that the central conductor 438 of the coaxial cable protrudes beyond a fastener free end 431.
FIG. 4C shows a compression type male F connector 400C. A connector body 446 arranged concentrically about a post 449 provides an annular cavity 448 for receiving metal braid 447 and jacket 445 of a coaxial cable 450. The body and a fastener 444 are rotatably engaged. Passing through a hollow interior of the post is coaxial cable dielectric 461 and coaxial cable center conductor 442. Cable fixation occurs when a connector outer shell 443 forces a collapsible ring 441 to press against the coaxial cable jacket as the shell is slid toward a fastener 444 of the connector.
FIG. 4D shows a crimp type male F connector utilizing a fixed pin 400D. A connector body 468 is arranged concentrically about an insulator 465 and a post 466 adjacent to the insulator. The post abuts the connector body at one end 463 and is spaced apart from the connector body at an opposed end creating an annular cavity 461 for receiving metal braid and jacket of a coaxial cable (not shown). The insulator 465 supports a center conductor such as a contact pin 462 and a fastener 464 rotatably engages the body. Cable fixation occurs when a crimp zone of the connector body 470 is forced against an outer jacket of a coaxial cable (not shown).
These prior art devices may frequently be found inadequately shielded as proliferation of RF devices such as cellular telephones crowd RF spectra and increase the chances RF ingress will adversely affect interconnected systems using coaxial cable such as cable television and satellite television signal distribution systems.
Persons of ordinary skill in the art have recognized that in cable television and satellite television systems (“CATV”), reduction of interfering radio frequency (“RF”) signals improves signal to noise ratio and helps to avoid saturated reverse amplifiers and related optical transmission that is a source of distortion.
Past efforts have limited some sources of the ingress of interfering RF signals into CATV systems. These efforts have included increased use of traditional connector shielding, multi-braid coaxial cables, connection tightening guidelines, increased use of traditional splitter case shielding, and high pass filters to limit low frequency spectrum interfering signal ingress in active home CATV systems.
Connectors used for home coaxial cable installations include F, IEC, MCX, and PAL type connectors. For example, in the home one will typically find a wall mounted female coaxial connector or a coaxial cable drop splitter or isolator for supplying a signal to the TV set, cable set-top box, or internet modem.
A significant location of unwanted RF signal and noise ingress into CATV systems is in the home. This occurs where the subscriber leaves a CATV connection such as a wall-mounted connector or coaxial cable drop connector disconnected/open. An open connector end exposes a normally metallically enclosed and shielded signal conductor and can be or contribute to a significant source of unwanted RF ingress.
As shown above, a CATV signal is typically supplied to a room via a wall mounted connector or in some cases a simple cable drop. These and similar cable interconnection points provide potential sources of unwanted RF signal ingress into the CATV system. As will be appreciated, multiple CATV connections in a home increase the likelihood that some connections will be left unused and open, making them a source of unwanted RF ingress. And, when subscribers move out of a home, CATV connections are typically left open, another situation that invites RF ingress in a CATV distribution system.
Known methods of eliminating unwanted RF ingress in a CATV system include adding a metal cover over each unused coaxial connector in the home or, adding a metal cover over the feeder coaxial connection at the home network box. But, the usual case is that unused home CATV connections are left active and without covers, a practice the cable television operators and the industry have accepted in lieu of making costly service calls associated with new tenants and/or providing the CATV connections in additional rooms.
The inventor's work in this area suggests current solutions for reducing unwanted RF ingress and egress resulting from open connectors are not successful and/or not widely used. Therefore, to the extent the CATV industry comes to recognize a need to further limit interfering RF ingress into CATV systems, it is desirable to have connectors that reduce RF ingress when they are left open.
Prior art exists which attempts to accomplish this goal but is frequently found to be prohibitively expensive, impractical, or unreliable. For example, U.S. Pat. No. 8,098,113 filed Oct. 9, 2009, discloses electronics that differentially cancel noise common to both the center conductor and shield and requires an electric power source. Such methods are relatively expensive compared with at least some embodiments of the present invention. They also have reliability limitations due to added electrical components such as semiconductors and/or passive devices.